The present invention relates to recordable media defect detection for recording systems, and particularly to methods and apparatus for detecting recording media defects in a recorder-reproducer drive system.
Defect detection is generally performed for high quality recordable media, such as magnetic storage discs, as part of the manufacturing process with a dedicated single disc tester. Such disc testers perform drop-in/drop-out testing over the entire disc with special defect detection patterns before the disc is assembled into an associated disc pack. The defect pattern may be a so-called "4F" type, comprising a high level (1)-low level (0) alternating series (101010...) to best reveal "drop-outs," or missing 1's in the reproduced signal at the highest possible data rate. Alternately, a direct current erase signal may be recorded to sense "drop-ins," or extra 1's, in the reproduced signal. Since the discs are tested before assembly into an associated disc pack and formatted with all its embedded servo information (in a fully-embedded disc drive), it is unfeasible to accurately transfer the exact location of defects to the drive. Furthermore, variability in gap width and electrical parameters between the single disc tester and the disc drive reduce the quality of defect detection performed in the single disc tester.
In-drive defect detection is generally limited to recording and reproducing data patterns in the same way that recording and reproducing is performed under normal use, and errors in the read process are used to identify defects in each sector. This procedure cannot accurately detect defects in the data preamble and sync areas of each sector.
Consequently, it is much more desirable to arrange a defect detection system which performs drop-in/drop-out testing and utilizes the recording system of the recorder/reproducer drive system in which the discs are actually used.